The invention relates to a method for separating off solid materials from a suspension.
Methods of the named kind are used to separate the largest portion of the solid material particles in a suspension from the suspension. The purpose of doing this can either be for the clarification of contaminated drain water or also for the recovery of solid material particles in a suspension for subsequent use, or for a combination of both these requirements. Floatation is a well suited method in the commonly occurring cases in which the quantity of the suspended solid materials is very low, such as for example approximately 0.1-1% . As is known, a foam or scum (floating sludge) is formed which contains the material to be separated out.
A typical application for the use of a method of this kind is the processing of contaminated waters in a paper factory. These waters often contain a residue of undesired solid material particles which have to be removed in order to better re-employ the water clarified in this way in the paper production. It is methods of this kind which have made it possible that today a considerable part of the water used in a paper factory must no longer be fed into the drain after use, but can be fed back in circulation.
Similar to gravitational sedimentation methods, floatation methods have the property that the suspension which is to be clarified must be subject to treatment for a long time, i.e., a relatively long dwell time is required for carrying out the method. Also as a rule, very large quantities of water must be prepared in this way. For these two reasons, the problem often arises of uniformly conveying large amounts of suspension free from undesired vortices. When this is not achieved, highly damaging short-circuiting currents form which lead to contamination of the water which is already clarified, or at least to an undesired shortening of the dwell time. In the past, highly complicated apparatuses were provided in order to avoid such loss effects. Alongside the disadvantage of the high price of such apparatuses, they also required complicated servicing and were easily contaminated.